The present invention relates to a thermal analysis apparatus, and in particular to thermogravimetry apparatus.
With thermogravimetry apparatus, samples are mounted on a sample holder on top of a plate located at the tip of a balance arm, and the thermogravity apparatus heats the sample using a furnace following a predetermined temperature program. Changes in the weight of the sample are then measured using the balance arm. If there is a change in the weight of the sample the balance arm tilts, moving away from the equilibrium position. The extent of the shifting away from the equilibrium position is electrically detected, and driving is performed so as to return the balance arm to the equilibrium position. The drive force at this point is measured as the change in the weight of the sample. For this reason, feedback control to return to the equilibrium position is always being carried out according to the extent of movement away from the equilibrium position of the balance arm.
When removing or mounting the sample, if a sudden balance arm tilt occurs greater than the response speed of the feedback controls trying to cause the balance arm to return to the equilibrium position, the feedback controls cause a state of oscillation, causing the balance arm to vibrate in a dramatic manner. This vibration can cause samples to be dropped, and balance arm damage etc. Especially when using an automatic sample conveyance apparatus in combination with the thermogravimetry apparatus, although mounting or removal of the sample is carried out with the automatic sample conveyance apparatus in a fixed position, if vibration occurs at this time, problems such as droppage due to failure to grab a sample and collision of the balance arm and the automatic sample conveyance apparatus may occur.
Conventionally, steps have been taken to mechanically fix the balance arm when mounting or removing the sample so as to prevent this type of problem occurring.
The following constraints exist with regards to the implementation of means to mechanically fix the balance arm when mounting the sample.
(1) The fixing means does not become a hindrance to the balance arm when measuring.
(2) The fixing means does not influence measurement precision.
(3) The fixing means can withstand the heat from the furnace or may be retracted to a position where heating may be withstood.
Because of the above constraints, fixing means have become objects containing a large number of moving parts, and tend to also have a large movement range. Such mechanical fixing means are expensive, occupy a large volume, and are an impediment to apparatus price reduction as well as size reduction. In addition, because such equipment contains mechanical moving parts, the likelihood of failure is high.
The present invention aims to provide a means for fixing and suppressing vibration of the balance arm when mounting or removing samples at a low price, while keeping footprint to a minimum.
The advantage of the present invention is provided with a balance arm having a sample holder, a detector for detecting an amount of shift of the balance arm from an equilibrium position, a control circuit for carrying out feedback control towards the equilibrium position of the balance arm, a driver for driving the balance arm towards the equilibrium position, an exchange stage detector for detecting when a sample is being changed, and a fixed output holding circuit for maintaining the output of the driver at a fixed level while the exchange stage is indicated by the exchange stage detector.